1. Field of the Invention
The present invention relates to an ionic current detection apparatus for an internal combustion engine capable of detecting at least the occurrence of misfiring, knocking or the like by detecting a change in the amount of ions generated by combustion of an air fuel mixture in the internal combustion engine.
2. Description of the Related Art
It is generally known that ions are generated when an air fuel mixture is burnt or combusted in cylinders of an internal combustion engine. Thus, using a probe arranged in each cylinder and impressed with a high voltage as a bias voltage, the ions thus generated can be observed as an ionic current. In addition, when there takes place knocking in an internal combustion engine, a vibration component of the knocking is superposed on the ionic current so that the occurrence of the knocking can be detected by extracting this vibration component (for example, see a first patent document: Japanese patent laid-open No. 2001-140740).
However, in the past, in ignition coils in an inline four-cylinder engine for example, the central axis of each ignition coil is arranged in such a manner that it becomes the same direction in which the central axes of adjacent ignition coils are arranged, and the ignition coils are fixed with respect to one another by the use of a holder or the like and then mounted on the engine.
Therefore, when an ignition coil for a cylinder other than the current firing cylinder or an ignition coil for the next firing cylinder is started to be energized, there is generated a false ionic current in the current firing cylinder for which an ionic current is now being detected, indicating as if combustion or knocking has taken place in the current firing cylinder. As a consequence, there arises a problem in that a false knock component signal is generated due to such a false ionic current thus detected, and hence an erroneous combustion pulse is generated due to the false knock pulse at this time, resulting in an incorrect combustion determination or an incorrect knock determination.